Medical electrical lead

ABSTRACT

An improved medical electrical lead is disclosed herein. The lead may include a longitudinally extending body having a distal end, a proximal end, a conductive element extending between the distal and proximal ends, and an electrode coupled to the conductive element utilizing a reflow process. The conductive element and electrode may comprise materials that are incompatible.

TECHNICAL FIELD

The present application relates to implantable medical devices and, moreparticularly, leads for electrical stimulators.

BACKGROUND

The human anatomy includes many types of tissues that can eithervoluntarily or involuntarily, perform certain functions. After disease,injury, or natural defects, certain tissues may no longer operate withingeneral anatomical norms. For example, after disease, injury, time, orcombinations thereof, the heart muscle may begin to experience certainfailures or deficiencies. Certain failures or deficiencies can becorrected or treated with implantable medical devices (IMDs), such asimplantable pacemakers, implantable cardioverter defibrillator (ICD)devices, cardiac resynchronization therapy defibrillator devices, orcombinations thereof. The electrical therapy produced by an IMD mayinclude, for example, pacing pulses, cardioverting pulses, and/ordefibrillator pulses to reverse arrhythmias (e.g. tachycardias andbradycardias) or to stimulate the contraction of cardiac tissue (e.g.cardiac pacing) to return the heart to its normal sinus rhythm.

In general, the IMDs include a battery and electronic circuitry, such asa pulse generator and/or a processor module, that are hermeticallysealed within a housing (generally referred to as the “can”). Animplantable lead interconnects the IMD and the heart. Typically, amedical electrical lead includes a flexible elongated body with one ormore insulated elongated conductors. Each conductor electrically couplesa sensing and/or a stimulation electrode of the lead to the electroniccircuitry through a connector module. Electrical signals are transmittedbetween the electrodes and the pulse generator. For an IMD, functionalimplant life time is, in part, determined by the energy delivered perpulse. The IMD will have a longer life if the energy delivered per pulsecan be maintained at a minimum. Designs of the lead and of theelectrodes which are used with the lead are influenced by the electricalsignal required for pacing stimulation. Physiologically, the IMD shouldbe capable of generating a signal with a sufficient magnitude todepolarize the excitable cells of the myocardium to initiatecontraction. The electrode shape, size, surface area, material andimpedance combine to determine the energy required of the IMD.

In the context of medical electrical leads, a tubular electrode maytypically be mounted around the exterior of an insulative lead body andcoupled to an elongated conductive coil within the lead body. Differentcombinations of materials have been proposed for the electrode andconductive coils in the lead construction. However, the inventors of thepresent disclosure have found that conventional techniques utilized injoining different combinations of materials present challenges in theconstruction of leads having different combinations of materials. Forexample, the techniques utilized in joining some of these materials havebeen found to result in formation of intermettalics when the materialsused have incompatible compounds. A property of intermettalics isbrittleness which results in cracks and uneven surfaces therebycompromising the electrical conductivity and mechanical integrity of thelead.

Some proposals to overcome the above and other disadvantages haveincluded cladding the conductive coil with a suitable material prior tocoupling with another component. For example, the conductive coil may becladded with the suitable material and the cladded portion of theconductor is then welded to the other component.

Therefore, there remains a need for an improved method of constructingan implantable lead having incompatible materials that are coupleddirectly, while maintaining the desired electrical conductivity andmechanical integrity.

BRIEF SUMMARY OF THE DISCLOSURE

An implantable medical lead is disclosed. It is generally desirable toprovide medical leads that have intact mechanical and electricalconnectivity.

Accordingly, in contrast to the conventional coupling techniques, thepresent disclosure provides exemplary construction and couplingtechniques for leads having various combinations of materials.

In one embodiment, the lead may include a longitudinally extending bodyhaving a distal end, a proximal end, a conductive element, such as acable, extending between the distal and proximal ends, and an outerjacket about the conductive element. At least one electrode is connectedto the conductive element. In some embodiments, the connection betweenthe conductive element and the electrode is achieved by reflowing aportion of the conductive element onto the electrode.

In some embodiments, the electrode is constructed of a first materialand the conductive element is constructed of a second material. Thefirst and second materials may be selected from materials consistingessentially of at least one of the following: tantalum, platinum, gold,iridium, rhenium, tungsten, ruthenium, depleted uranium, cobalt,chromium, titanium, aluminum, vanadium, chromium, nickel, molybdenum,iron, copper, silver, gold, stainless steel, magnesium-nickel, palladiumand alloys thereof.

The present disclosure also relates to methods of manufacturing medicalelectrical leads. In one embodiment, the method includes: providing alongitudinally extending conductive element and providing an outerjacket about the conductive element. In an embodiment, a tubularelectrode is positioned over and attached to the outer jacket. Thetubular electrode is coupled to the conductive element. In someembodiments, the coupling is achieved by heating the conductive elementto a molten state and manipulating it to flow over the electrode.

The foregoing has outlined rather broadly certain features and/ortechnical advantages in order that the detailed description that followsmay be better understood. Additional features and/or advantages will bedescribed hereinafter which form the subject of the claims. It should beappreciated by those skilled in the art that the conception and specificembodiment disclosed may be readily utilized as a basis for modifying ordesigning other structures for carrying out the same purposes. It shouldalso be realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the appendedclaims. The novel features, both as to organization and method ofoperation, together with further objects and advantages will be betterunderstood from the following description when considered in connectionwith the accompanying figures. It is to be expressly understood,however, that each of the figures is provided for the purpose ofillustration and description only and is not intended as a definition ofthe limits of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will hereinafter be described inconjunction with the following drawings wherein like reference numeralsdenote like elements throughout.

FIG. 1 is a conceptual diagram illustrating an example therapy system 10that may be used to provide therapy to a heart of a patient.

FIG. 2 is a conceptual diagram illustrating an implantable medicaldevice and leads of therapy system 10 in greater detail.

FIG. 3 is a conceptual diagram illustrating another exemplary therapysystem.

FIGS. 4A and 4B depict two exemplary embodiments of lead bodyconstruction that may be used in connection with the medical electricalleads of the present disclosure.

FIGS. 5 and 6 show an exemplary embodiment of a lead sub-assembly of alead constructed in accordance with embodiments of the presentdisclosure.

FIG. 7 is a cutaway perspective view of the lead sub-assembly as shownin FIG. 6.

FIGS. 8A-8B are plan views each illustrating a step of an assembly of aportion of a lead sub-assembly according to embodiments of the presentdisclosure.

FIG. 9 illustrates a longitudinal section view of a lead assemblyaccording to an embodiment of the present disclosure.

FIG. 10 is a flowchart illustrating a fabrication process for theconstruction of a lead as described in conjunction with FIGS. 5-7.

FIGS. 11A-C are scanning electron micrograph photographs of portions oftwo prototype lead bodies.

DETAILED DESCRIPTION OF THE DISCLOSURE

In the following detailed description, reference is made to theaccompanying figures of the drawing which form a part hereof, and inwhich are shown, by way of illustration, specific embodiments. It is tobe understood that other embodiments may be utilized and structuralchanges may be made without departing from the scope of the presentdisclosure.

FIG. 1 is a conceptual diagram illustrating an example therapy system 10that may be used to provide therapy to heart 12 of patient 14. Patient14 ordinarily, but not necessarily, will be a human. Therapy system 10includes IMD 16, which is coupled to leads 18, 20, and 22, andprogrammer 24. IMD 16 may be, for example, an implantable pacemaker,cardioverter, and/or defibrillator that provides electrical signals toheart 12 via electrodes coupled to one or more of leads 18, 20, and 22.Each of leads 18, 20 and 22 may carry one or a set of electrodes. Theelectrode may extend about the circumference of each of leads 18, 20,and 22 and is positioned at a respective axial position along the lengthof each of the lead 18, 20, and 22.

Leads 18, 20, 22 extend into the heart 12 of patient 14 to senseelectrical activity of heart 12 and/or deliver electrical stimulation toheart 12. In the example shown in FIG. 1, right ventricular (RV) lead 18extends through one or more veins (not shown), the superior vena cava(not shown), and right atrium 26, and into right ventricle 28. Leftventricular (LV) coronary sinus lead 20 extends through one or moreveins, the vena cava, right atrium 26, and into the coronary sinus 30 toa region adjacent to the free wall of left ventricle 32 of heart 12.Right atrial (RA) lead 22 extends through one or more veins and the venacava, and into the right atrium 26 of heart 12.

IMD 16 may sense electrical signals attendant to the depolarization andrepolarization of heart 12 via electrodes (not shown in FIG. 1) coupledto at least one of the leads 18, 20, 22. In some examples, IMD 16provides pacing pulses to heart 12 based on the electrical signalssensed within heart 12. The configurations of electrodes used by IMD 16for sensing and pacing may be unipolar or bipolar. IMD 16 may alsoprovide defibrillation therapy and/or cardioversion therapy viaelectrodes located on at least one of the leads 18, 20, 22. IMD 16 maydetect arrhythmia of heart 12, such as fibrillation of ventricles 28 and32, and deliver defibrillation therapy to heart 12 in the form ofelectrical pulses. In some examples, IMD 16 may be programmed to delivera progression of therapies, e.g., pulses with increasing energy levels,until a fibrillation of heart 12 is stopped. IMD 16 detects fibrillationemploying one or more fibrillation detection techniques known in theart.

In some examples, programmer 24 may be a handheld computing device or acomputer workstation. Programmer 24 may include a user interface thatreceives input from a user. The user interface may include, for example,a keypad and a display, which may for example, be a cathode ray tube(CRT) display, a liquid crystal display (LCD) or light emitting diode(LED) display. The keypad may take the form of an alphanumeric keypad ora reduced set of keys associated with particular functions. Programmer24 can additionally or alternatively include a peripheral pointingdevice, such as a mouse, via which a user may interact with the userinterface. In some embodiments, a display of programmer 24 may include atouch screen display, and a user may interact with programmer 24 via thedisplay.

A user, such as a physician, technician, or other clinician, mayinteract with programmer 24 to communicate with IMD 16. For example, theuser may interact with programmer 24 to retrieve physiological ordiagnostic information from IMD 16. A user may also interact withprogrammer 24 to program IMD 16, e.g., select values for operationalparameters of the IMD.

For example, the user may use programmer 24 to retrieve information fromIMD 16 regarding the rhythm of heart 12, trends therein over time, ortachyarrhythmia episodes. As another example, the user may useprogrammer 24 to retrieve information from IMD 16 regarding other sensedphysiological parameters of patient 14, such as intracardiac orintravascular pressure, activity, posture, respiration, or thoracicimpedance. As another example, the user may use programmer 24 toretrieve information from IMD 16 regarding the performance or integrityof IMD 16 or other components of system 10, such as leads 18, 20, and22, or a power source of IMD 16.

The user may use programmer 24 to program a therapy progression, selectelectrodes used to deliver defibrillation shocks, select waveforms forthe defibrillation shock, or select or configure a fibrillationdetection algorithm for IMD 16. The user may also use programmer 24 toprogram aspects of other therapies provided by IMD 16, such ascardioversion or pacing therapies. In some examples, the user mayactivate certain features of IMD 16 by entering a single command viaprogrammer 24, such as depression of a single key or combination of keysof a keypad or a single point-and-select action with a pointing device.

IMD 16 and programmer 24 may communicate via wireless communicationusing any techniques known in the art. Examples of communicationtechniques may include, for example, low frequency or radiofrequency(RF) telemetry, but other techniques are also contemplated. In someexamples, programmer 24 may include a programming head that may beplaced proximate to the patient's body near the IMD 16 implant site inorder to improve the quality or security of communication between IMD 16and programmer 24.

FIG. 2 is a conceptual diagram illustrating IMD 16 and leads 18, 20, 22of therapy system 10 in greater detail. Leads 18, 20, 22 may beelectrically coupled to a stimulation generator, a sensing module, orother modules of IMD 16 via connector block 34. In some examples,proximal ends of leads 18, 20, 22 may include electrical contacts thatelectrically couple to respective electrical contacts within connectorblock 34. In addition, in some examples, leads 18, 20, 22 may bemechanically coupled to connector block 34 with the aid of set screws,connection pins or another suitable mechanical coupling mechanism.

Each of the leads 18, 20, 22 includes an elongated insulative lead body,which may carry a number of concentric coiled conductors separated fromone another by tubular insulative sheaths. In the illustrated example, apressure sensor 38 and bipolar electrodes 40 and 42 are locatedproximate to a distal end of lead 18. In addition, bipolar electrodes 44and 46 are located proximate to a distal end of lead 20 and bipolarelectrodes 48 and 50 are located proximate to a distal end of lead 22.In FIG. 2, pressure sensor 38 is disposed in right ventricle 28.Pressure sensor 30 may respond to an absolute pressure inside rightventricle 28, and may be, for example, a capacitive or piezoelectricabsolute pressure sensor. In other examples, pressure sensor 30 may bepositioned within other regions of heart 12 and may monitor pressurewithin one or more of the other regions of heart 12, or may bepositioned elsewhere within or proximate to the cardiovascular system ofpatient 14 to monitor cardiovascular pressure associated with mechanicalcontraction of the heart.

Among the electrodes, some of the electrodes may be provided in the formof coiled electrodes that form a helix, while other electrodes may beprovided in different forms. Further, some of the electrodes may beprovided in the form of tubular electrode sub-assemblies that can bepre-fabricated and positioned over the body of leads 18, 20, 22, wherethey are attached and where electrical connections with conductiveelements within the leads 18, 20, 22 can be made. For example,electrodes 40, 44 and 48 may take the form of ring electrodes, andelectrodes 42, 46 and 50 may take the form of extendable helix tipelectrodes mounted retractably within insulative electrode heads 52, 54and 56, respectively. Each of the electrodes 40, 42, 44, 46, 48 and 50may be electrically coupled to a respective one of the coiled conductorswithin the lead body of its associated lead 18, 20, 22, and therebycoupled to respective ones of the electrical contacts on the proximalend of leads 18, 20 and 22.

Electrodes 40, 42, 44, 46, 48 and 50 may sense electrical signalsattendant to the depolarization and repolarization of heart 12. Theelectrical signals are conducted to IMD 16 via the respective leads 18,20, 22. In some examples, IMD 16 also delivers pacing pulses viaelectrodes 40, 42, 44, 46, 48 and 50 to cause depolarization of cardiactissue of heart 12. In some examples, as illustrated in FIG. 2, IMD 16includes one or more housing electrodes, such as housing electrode 58,which may be formed integrally with an outer surface ofhermetically-sealed housing 60 of IMD 16 or otherwise coupled to housing60. In some examples, housing electrode 58 is defined by an uninsulatedportion of an outward facing portion of housing 60 of IMD 16. Otherdivision between insulated and uninsulated portions of housing 60 may beemployed to define two or more housing electrodes. In some examples,housing electrode 58 comprises substantially all of housing 60. Any ofthe electrodes 40, 42, 44, 46, 48 and 50 may be used for unipolarsensing or pacing in combination with housing electrode 58. As is knownin the art, housing 60 may enclose a stimulation generator thatgenerates cardiac pacing pulses and defibrillation or cardioversionshocks, as well as a sensing module for monitoring the patient's heartrhythm.

Leads 18, 20, 22 also include elongated electrodes 62, 64, 66,respectively, which may take the form of a coil. IMD 16 may deliverdefibrillation shocks to heart 12 via any combination of elongatedelectrodes 62, 64, 66, and housing electrode 58. Electrodes 58, 62, 64,66 may also be used to deliver cardioversion pulses to heart 12.Electrodes 62, 64, 66 may be fabricated from any suitable electricallyconductive material, such as, but not limited to, platinum, platinumalloy or other materials known to be usable in implantabledefibrillation electrodes.

Pressure sensor 38 may be coupled to one or more coiled conductorswithin lead 18. In FIG. 2, pressure sensor 38 is located more distallyon lead 18 than elongated electrode 62. In other examples, pressuresensor 38 may be positioned more proximally than elongated electrode 62,rather than distal to electrode 62. Further, pressure sensor 38 may becoupled to another one of the leads 20, 22 in other examples, or to alead other than leads 18, 20, 22 carrying stimulation and senseelectrodes.

The configuration of therapy system 10 illustrated in FIGS. 1 and 2 ismerely one example. In other examples, a therapy system may includeepicardial leads and/or patch electrodes instead of or in addition tothe transvenous leads 18, 20, 22 illustrated in FIG. 1. Further, IMD 16need not be implanted within patient 14. In examples in which IMD 16 isnot implanted in patient 14, IMD 16 may deliver defibrillation shocksand other therapies to heart 12 via percutaneous leads that extendthrough the skin of patient 14 to a variety of positions within oroutside of heart 12.

In other examples of therapy systems that provide electrical stimulationtherapy to heart 12, a therapy system may include any suitable number ofleads coupled to IMD 16, and each of the leads may extend to anylocation within or proximate to heart 12. For example, other examples oftherapy systems may include three transvenous leads located asillustrated in FIGS. 1 and 2, and an additional lead located within orproximate to left atrium 33. Other examples of therapy systems mayinclude a single lead that extends from IMD 16 into right atrium 26 orright ventricle 28, or two leads that extend into a respective one ofthe right ventricle 26 and right atrium 28. An example of this type oftherapy system is shown in FIG. 3.

FIG. 3 is a conceptual diagram illustrating another example of therapysystem 70, which is similar to therapy system 10 of FIGS. 1-2, butincludes two leads 18, 22, rather than three leads. Leads 18, 22 areimplanted within right ventricle 28 and right atrium 26, respectively.Therapy system 70 shown in FIG. 3 may be useful for providingdefibrillation and pacing pulses to heart 12.

FIGS. 4A and 4B depict two exemplary embodiments of lead bodyconstruction that may be used in connection with the medical electricalleads 18 and 22 of the present disclosure. The illustrative embodimentsof FIGS. 4A and 4B depict portions of leads 18 and 22, respectively,before electrodes are coupled thereto. It should, however, be noted thatthe construction of the lead bodies discussed with respect to leads 18and 22 may be employed interchangeably or together on any of theexemplary leads 18, 20, and 22. Referring to FIG. 4A, one example of alead body is depicted (with respect to lead 18) having conductiveelements 112 a, 112 c that are provided in a wrapped configuration. Thedepicted lead 18 also comprises one or more internal jackets 130 with anouter jacket 140 that surrounds the one or more internal jackets 130.According to embodiments of the present disclosure at least oneconductive fitting (shown in FIG. 7) is coupled to each of conductiveelements 112 a and 112 c. That coupling may be made by a variety oftechniques, with at least some potentially suitable connectiontechniques being described in U.S. Patent Application Publication Nos.U.S. 2005/0240252 (Boser et al.); U.S. 2005/0113898 (Honeck et al.),incorporated herein by reference in their entirety.

FIG. 4B depicts another lead body (of exemplary lead 22) that includesconductive elements 112 b and 112 d that extend linearly along thelength of the lead body. The conductive elements 112 b and 112 d may belocated between an inner jacket 130 and an outer jacket 140. In someembodiments, both wrapped (112 a, 112 c) and linear (112 b, 112 d)conductive elements may be provided in the same lead body. In anotherembodiment (not shown), an exemplary lead body that may be used is amulti-lumen tubular structure (symmetric or asymmetric), which is knownto those skilled in the art.

An example of an appropriate material for the conductive elements 112 a,112 b, 112 c and 112 d employed by embodiments of the present disclosureis an MP35N alloy with one or more of the conductive elements furtherincluding a low resistance core, for example silver. Other examples ofappropriate material include tantalum, platinum, gold, iridium, rhenium,tungsten, ruthenium, depleted uranium, cobalt, chromium, titanium,aluminum, vanadium, chromium, nickel, molybdenum, iron, copper, silver,gold, stainless steel, magnesium-nickel, palladium. It should be notedthat the listing of materials is not intended to be limiting and otherexemplary materials may comprise combinations of the aforementionedmaterials and/or alloys thereof. According to some embodiments of thepresent disclosure, internal jacket 130 and external jacket 140 areformed from an insulative material, examples of which includefluoropolymers, silicones, and polyurethanes. Specific examples of anappropriate material for internal jacket 130 and external jacket 140 areEthylene tetrafluoroethylene (ETFE) and PolyEtherEtherKetone (PEEK). Itshould be noted that according to some embodiments, when the conductiveelements 112 a, 112 b, 112 c and 112 d are positioned along internaljacket 130, they can be embedded in an outer surface of the internaljacket 130.

Turning to FIGS. 5 and 6, an exemplary embodiment of a lead sub-assembly250 of any of leads 18, 20 and 22 is depicted, where an electrodesub-assembly 350 of any of electrodes 40, 44 and 48 is positioned overexternal jacket 140. The electrode 350 is preferably embedded in anouter surface 260 of external jacket 140 to a depth that is sufficientto mechanically and electrically couple the electrode 350 to theappropriate conductive element 112 a, 112 c directly or through aconductive fitting (FIG. 7). At least a portion of the outer surface 272of the electrode 350 is exposed proximate to the outer surface 260 suchthat the electrode 350 can be placed in electrical communication withtissue and/or fluids surrounding the electrode sub-assembly 350.

Another optional feature depicted in FIGS. 5 and 6 is that the lead bodyof lead sub-assembly 250 may be constructed with a variable diametersuch that the area in which the electrode sub-assembly 350 is positionedhas a reduced size as compared to other portions of the lead body. Forexample, the lead sub-assembly 250 may include a shoulder 218 as seen inFIG. 6 where the diameter of the lead body decreases. The diameter ofthe lead body may be increased on the opposite end of the electrodesub-assembly 350 by optionally including a sleeve 219 or other structureto increase the size of the lead. Such a construction can be used toprovide an isodiametric lead, although other constructions could also beused to compensate for the thickness of the electrode sub-assembly 350.

The electrode 350 may, in some embodiments, be formed in the shape of acoil with one or more wraps or coils and using a wire element having arectangular cross-section as depicted in FIG. 6, although coiledelectrodes in other embodiments may be formed using wire elements havingany selected shape (e.g., round, oval, elliptical, etc.)

FIG. 7 is a cutaway perspective view of the lead sub-assembly 250 asshown in FIG. 6. According to the embodiment, conductive element 112 ais coupled to electrode 350 via a conductive fitting 320; according tothis embodiment, conductive fitting 320 is coupled to conductive element112 a prior to positioning the conductive element in the lead body. Inalternate embodiments, fitting 320 may be coupled to conductive element112 a after conductive element 112 a has been positioned in internaljacket 130. A portion of the aforementioned internal jacket 130surrounding conductive element 112 a is removed to expose conductiveelement 112 a in order to couple fitting 320 to conductive element 112a. Means for removing the insulation in proximity to the fitting arewell known to those skilled in the art and include but are not limitedto, mechanical and laser stripping. It should be noted that althoughFIG. 7 shows the insulative portion removed for coupling with fitting320, other types of fittings having internal features to penetrateinternal jacket 130 may be employed so that internal jacket 130 need notbe removed for coupling. Furthermore, according to other embodiments ofthe present disclosure, electrode 350 is coupled directly to conductiveelement 112 a.

FIGS. 8A-8B are plan views, each illustrating a step of an assembly oflead sub-assembly portions according to embodiments of the presentdisclosure. For ease of discussion, the illustration of the assembly oflead sub-assemblies 450 a, 450 b has been simplified to include thecomponents that are pertinent to the discussion and those skilled in theart will recognize that several other components can be included.

Accordingly, FIG. 8A depicts lead sub-assembly 450 a having anuninsulated portion of a conductive element 412 a. An electrode 452 a ispositioned on the conductive element 412 a at a desired mountinglocation and may be pressed against lead subassembly 450 a per arrow A.The conductive element 412 a is “reflown” over the electrode 452 a toachieve mechanical coupling. As used herein, a reflow process refers toany known technique that permits the heating of the conductive element412 a to a melting point such that the resulting molten substance can bemanipulated as desired during construction. Exemplary techniquesutilizing the reflow process include laser welding where the laser beamis projected at a pre-selected location on the conductive element 412 aas will be discussed further in conjunction with FIG. 9. The laser beamhas a frequency in the range of about 5-15 Hz, with an energy levelbetween 0.5-3 J and is applied for a duration in the range of 0.5-3.0ms.

FIG. 8B is a section view of lead sub-assembly 450 b according to analternate embodiment of the present disclosure. According to thisembodiment, a conductive fitting 454 is coupled to a conductive element412 b. The material used for construction of the conductive fitting 454is preferably identical to, but may also be selected from a variety ofmaterials that are compatible with, the material used to construct theconductive element 412 b. Often, compounds having dissimilar chemicalproperties will exhibit cracking and other imperfections when fusedtogether through conventional bonding techniques; in other words, theyare incompatible. Thus, as used in this disclosure, compatibility refersto the ability of two compounds to fuse together without compromisingthe structural integrity of the bonding junction. With continuedreference to FIG. 8B, an electrode 452 b is positioned at a desiredmounting location on the conductive fitting 454. A portion of theconductive fitting 454 is reflown to achieve the coupling to theelectrode 452 b. In alternative embodiments, the material of conductivefitting 454 may be selected to be compatible with the material of anelectrode 452 b. In such embodiments, the reflow process will beutilized to couple the conductive fitting 454 to the conductive element412 b.

FIG. 9 illustrates a longitudinal cross-sectional view of a leadassembly according to an embodiment of the present disclosure. Theillustration of FIG. 9 depicts a conductive element 512 that is placedadjacent to electrode 552 in anticipation of the coupling process inaccordance with one embodiment of the present disclosure. Generally, thecoupling involves a reflow process, where a first material having alower melting point relative to the melting point of a second materialis heated to a melting point and the molten substance is manipulated toflow over and form a covering layer on a portion of the second material.Thus, although the temperature of the second material will rise, thematerial remains in a solid state because of its relatively highermelting point. In the exemplary embodiment, a laser beam is directed atthe conductive element 512, generally in the direction of arrow B, tocause it to heat up and reach a molten state. The resulting moltensubstance of conductive element 512 may then be manipulated onto theelectrode 552 through physical relocation or by positioning the assemblyto enable gravitational force to influence the molten substance to flowover the electrode 552. It should be noted that illustration anddescription of various components typically utilized for construction ofa medical lead have been omitted for ease of discussion. Further detailson the omitted components and description are known to those of skill inthe art and exemplary descriptions can be found in U.S. Pat. No.5,935,159 (Cross, Jr., et al.), incorporated herein by reference in itsentirety.

FIG. 10 is a flowchart illustrating a fabrication process for theconstruction of a lead as described in conjunction with FIGS. 5-7. Inone embodiment, a lead sub-assembly 250 may be provided in apreassembled state to include a conductive element 112 a, an internaljacket 130 surrounding the conductive element 112 a, and an externaljacket 140 extending about the internal jacket 130 [block 600]. Inexemplary embodiments, the lead sub-assembly 250 may be prefabricatedand procured on bulk spools. The appropriate length of prefabricatedlead sub-assembly 250 is first cut from a bulk spool of material [block605]. Electrode and/or connector termination locations are prepared atthe appropriate locations of the lead sub-assembly 250 according to thetype of lead and electrode configuration to be assembled [block 610].For example, laser ablation may be used to remove the various layers ofthe external jacket 140 and internal jacket 130 covering the conductiveelement 112 a. In alternate embodiments, a conductive fitting 320 may becoupled to the conductive element 112 a during pre-fabrication of leadsub-assembly 250 in which case removal of the insulative jackets 130,140 exposes the fitting 320; or, the conductive fitting 320 is coupledafter removal of the insulative jackets 130, 140 [block 615]. Exemplarytechniques such as crimping, welding, brazing, soldering or electricallyconductive epoxy may be used to join the conductive fitting 320 to theconductive element 112 a.

An electrode 350 is positioned adjacent to the appropriate electrodetermination location (either on the conductive element 112 a for directcoupling, or on the conductive fitting 320) [block 620]. Optionally,portions of the electrode 350 and conductive element 112 a (orconductive fitting 320, as appropriate) may be placed under compressionto prevent movement prior to completion of the coupling [block 625]. Thematerial of the conductive element 112 a (or conductive fitting 320, asappropriate) is then reflowed to cause a coating of the material tocover the electrode 350 [block 630]. The reflow may include heating thematerial of the conductive element 112 a to a temperature that causesthe material to melt. Examples of techniques to heat the material mayinclude laser welding and any other techniques that can be employed tofocus an energy source primarily on the conductive element 112 a. Oncethe material of the conductive element 112 a reaches a molten state, thematerial is manipulated to provide a coating on a portion of theelectrode 350. Subsequently, the assembly comprising the electrode 350and the coating or layer of material of the conductive element 112 a ispermitted to settle and fuse together [block 635]. According to onemethod of the present disclosure, the assembly may be cooled back to aroom temperature.

In alternate embodiments, the external jacket 140 is placed subsequentto the construction of the fused assembly; alternatively, any additionalcomponents that could not be installed, for example, o-ring seals,steroid plugs, suture sleeves, etc., may then be installed [block 640].

As those skilled in the art will appreciate, the above discussion can beimplemented in conjunction with new or known techniques of manufacturingmedical electrical leads. For example, the lead sub-assembly 250 may beprovided as a pre-assembled helical sub-assembly further including aremovable core wire (not shown) contained as a build mandrel or buildwire. The core wire may provide support to the lead sub-assembly 250during handling in manufacturing. More importantly, the core wire may bepulled tightly in assembly jigs and fixtures, providing stable,straight, and precisely positionable helical lead sub-assembliesrequired for modular automated manufacturing processes. The core wire iseasily withdrawn from the lead body or, more specifically, the helicallead sub-assembly 250, whenever required.

In some embodiments, the above-described method of manufacture is highlyadvantageous at least in part due to the structural integrity of theresulting conductive element 112 a-to-electrode 350 junction. Prototypelead bodies built employing the construction techniques disclosed hereinwere tested and proven to have superior flex fatigue and tensilestrength properties in addition to maintaining the required structuralintegrity, as compared to leads built with conventional techniques thatwere found to even exhibit multiple cracks.

FIGS. 11A-C are scanning electron micrograph photographs of portions oftwo prototype lead bodies. The illustrative FIGS. 11A-D depict the outersurface of the junction between conductive elements 812 a, 812 b andelectrodes 850 a, 850 b. Both leads were constructed from the samematerial; the material used for construction of conductive coils 812 a,812 b was comprised of a cobalt alloy, MP35N having chemical structure35Ni-35Co-20Cr-10Mo, whereas the material used for construction of theelectrodes 850 a, 850 b was a tantalum alloy, with the chemicalstructure Ta-10Nb-6W. The prototype lead depicted in FIGS. 11A-B wasconstructed in accordance with conventional techniques whereas theprototype lead depicted in FIG. 11C was constructed in accordance withthe exemplary techniques disclosed above.

Turning to FIG. 11A, the photograph shows a prototype lead 820 a thatexhibits cracks 802 resulting from the coupling, which in this test wasutilized a conventional full fusion weld. FIG. 11B depicts an enlargedview of the cracks 802 formed on the prototype lead of FIG. 11A. Asillustrated, the mechanical integrity of the prototype lead 820 a isseverely compromised by the cracks 802.

In contrast to the prototype lead 820 a of FIG. 11A, the photograph inFIG. 11C depicts a prototype lead 820 b that exhibited no visibledeformation. FIG. 11C illustrates that the structural integrity of theresulting fused assembly was maintained. From these results, it isapparent that the construction techniques of the present disclosureprovide a robust medical electrical lead with desirable structuralintegrity that offers superior flexibility and durability as compared toconventional construction techniques.

Although the present disclosure has been described with reference topreferred embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the disclosure. For example, although the disclosuregenerally relates to leads in which the conductors are coupled toelectrodes, it should be understood that the construction techniques ofthe present disclosure are equally applicable to leads carrying othertypes of sensors, such as pressure sensors, temperature sensors and thelike, as well as being applicable to leads which carry other types ofelectrically powered devices.

What is claimed is:
 1. A method for manufacturing an implantable medicalelectrical lead device, comprising: providing a lead sub-assembly havingan electrode, an elongate conductor and a first insulative layercovering the elongate conductor; exposing a portion of the elongateconductor at a predetermined location; positioning an electrode adjacentto the exposed conductor; reflowing the exposed conductor into a moltenstate; manipulating the reflown exposed conductor to cover a portion ofthe electrode.
 2. The method of claim 1, wherein the elongate conductorhas a first melting point and the electrode has a second melting pointthat is higher than the first melting point.
 3. The method of claim 1,wherein reflowing the exposed conductor is performed by focusing a laserbeam on the elongate conductor, the laser beam having sufficient energyto melt the elongate conductor but not the electrode.
 4. The method ofclaim 1, wherein reflowing the exposed conductor is performed byresistance welding.
 5. An implantable medical electrical lead device,comprising: a lead body having a length between a proximal end and adistal end, wherein the lead body defines a longitudinal axis extendingbetween the proximal end and the distal end; a conductive elementlocated within an interior of the lead body and extending along thelongitudinal axis for at least a portion of the length of the lead body,wherein the conductive element has a first thermal melting point; and anelectrode having a second thermal melting point that is higher than thefirst thermal melting point that is positioned over the exterior surfaceof the lead body and bonded to the conductive element at a couplingjoint, wherein the coupling joint is formed by reflowing the conductiveelement onto the electrode.
 6. The implantable medical device lead ofclaim 5, wherein the conductive element is constructed of a firstmaterial and the electrode is constructed of a second material.
 7. Theimplantable medical device lead of claim 5, wherein the first materialconsists essentially of at least one of the following: tantalum,platinum, gold, iridium, rhenium, tungsten, ruthenium, depleted uranium,cobalt, chromium, titanium, aluminum, vanadium, chromium, nickel,molybdenum, iron, copper, silver, gold, stainless steel,magnesium-nickel, palladium and alloys thereof.
 8. The implantablemedical device lead of claim 7, wherein the first material consistsessentially of a cobalt-based alloy.
 9. The implantable medical devicelead of claim 5, wherein the second material consists essentially of atleast one of the following: tantalum, platinum, gold, iridium, rhenium,tungsten, ruthenium, depleted uranium, cobalt, chromium, titanium,aluminum, vanadium, chromium, nickel, molybdenum, iron, copper, silver,gold, stainless steel, magnesium-nickel, palladium and alloys thereof.10. The implantable medical device lead of claim 9, wherein the secondmaterial consists essentially of a tantalum alloy.
 11. The implantablemedical device lead of claim 5, wherein the reflow of the conductiveelement onto the electrode is formed by welding.
 12. The implantablemedical device lead of claim 11, wherein the welding process includesapplication of a laser beam having a frequency in the range of about5-15 Hz, with an energy level between 0.5-3 J and is applied for aduration in the range of 0.5-3.0 ms
 13. A method for manufacturing animplantable medical electrical lead device, comprising: providing a leadsub-assembly comprising an elongate conductor, an electrode and a firstinsulative layer, wherein the elongate conductor has a first thermalmelting point and the electrode has a second thermal melting point thatis higher than the first thermal melting point; covering at least aportion of the elongate conductor with the first insulative layer toform an elongate device body; positioning the electrode at apredetermined location on the elongate conductor; and coupling theelectrode to the elongate conductor, wherein the coupling includesreflowing the material of the elongate conductor onto the electrode. 14.The method of claim 13, further comprising: providing a conductivefitting; and coupling the conductive fitting to the elongate conductorat the predetermined location prior to positioning the electrode at thepredetermined location, wherein the electrode is directly coupled to theconductive fitting.
 15. The method of claim 13, further comprising:providing a second insulative layer; and covering the elongate devicebody with the second insulative body.
 16. The method of claim 13,wherein the elongate conductor comprises a first material and theelectrode comprises a second material.
 17. The method of claim 16,wherein the first material consists essentially of at least one of thefollowing: tantalum, platinum, gold, iridium, rhenium, tungsten,ruthenium, depleted uranium, cobalt, chromium, titanium, aluminum,vanadium, chromium, nickel, molybdenum, iron, copper, silver, gold,stainless steel, magnesium-nickel, palladium and alloys thereof.
 18. Themethod of claim 16, wherein the first material consists essentially of acobalt-based alloy.
 19. The method of claim 16, wherein the secondmaterial consists essentially of at least one of the following:tantalum, platinum, gold, iridium, rhenium, tungsten, ruthenium,depleted uranium, cobalt, chromium, titanium, aluminum, vanadium,chromium, nickel, molybdenum, iron, copper, silver, gold, stainlesssteel, magnesium-nickel, palladium and alloys thereof.
 20. The method ofclaim 16, wherein the second material consists essentially of tantalum.21. The method of claim 13, further comprising providing an openingthrough the first insulative layer in proximity to the predeterminedlocation prior to positioning the electrode.
 22. The method of claim 21,wherein providing the opening comprises forming the opening by means ofmechanical cutting.
 23. The method of claim 21, wherein providing theopening comprises forming the opening by means of thermal cutting. 24.The method of claim 13, wherein coupling the electrode comprises meltingthe elongate conductor and manipulating the molten substance to cover aportion of the electrode.
 25. The method of claim 13, wherein reflowingthe exposed conductor is performed by resistance welding.